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The world is a strange place filled with astonishing and bizarre animals. Among the strangest creatures are those which are transparent*—animals which barely seem to be there because the tissues that make up their bodies are permeable to light.  There are transparent catfish, transparent insects, transparent crustaceans, and even transparent frogs (to say nothing of cnidarians, the majority of which are transparent!).  Today’s post however concerns transparent mollusks.  In addition to having transparent bodies some of these incredible invertebrates have transparent shells, can invert their bodies, or can glow.  Check them out:

The Glass Squid (Teuthowenia pellucida)

The Glass Squid (Teuthowenia pellucida)

The Glass Squid (Teuthowenia pellucida) also known as the googly-eyed glass squid lives throughout the oceans of the southern hemisphere.  The creature is about 200 millimeters (8 inches) long and has light organs on its eyes.  Although transparent it has a bluish cast and it possesses the ability to roll into a ball or to inflate itself.  These tricks do not always work and the little squid is frequently eaten by weird deep-sea fish and sharks.

Zospeum tholussum

Zospeum tholussum

Recently discovered in a huge cave system in Croatia,  Zospeum tholussum, is a small delicate snail with a transparent shell.


This pterotracheid heteropod mollusk is a member of the Carinaria genus.  It lives in the open ocean and flaps through the water scooping up plankton in a modified snail foot. Just as its snail foot has changed into a swimming/harvesting organ, the mollusk’s shell has shrunk into near nonexistence.

0corolla (calceola)Above is an unknown pteropod (possibly of the genus Corolla), which was photographed near Oceanographer Canyon off the coast of Massachusetts.

Vitrelladonella Richardi

Vitrelladonella Richardi

Vitrelladonella Richardi is a deepwater pelagic octopus found in tropical and subtropical waters around the world.  The little octopus only measures 80cm (2.6ft) in length.  Like many of these almost invisible mollusks very little is known about how it lives, but it is certainly beautiful in a very alien and otherworldly way.

*The author of this opinion piece is opaque.  His opinion may not represent the larger community of organisms.

Clione or “sea angels” swimming in a Tokyo aquarium (Photo by REUTERS/Kimimasa Mayama)

In terms of taxonomical diversity the gastropods are second most diverse class of animals on Earth (outnumbered only by the teeming class Insecta of the other great invertebrate phylum Arthropoda).  This means that there are some deeply strange arthropods out there. While we traditionally think of gastropods as snails and slugs there are odd subcategories of these creatures, like the subject of today’s post, sea angels (of the clade Gymnosomata).

A “Sea Angel” (Clione limacina)

Sea angels consist of six different families of pelagic marine opisthobranch gastropod molluscs.  Gastropods are named for their famous foot (the name means “stomach-foot”–a misnomer since gastropods all have true stomachs elsewhere) however the name is even more inappropriate for sea angels.  In these free-smimming predators, the gastropod foot, so familiar to us as seen on snails, has evolved into a pair of delicate wings for swimming through the water. Sea angels are very small: the largest species only reach 5 cm (2 inches) in length and most varieties are much more miniscule.  They prey on other tiny creatures swimming among the plankton—particularly other smaller slower species of gelatinous mollusks.

A hunting sea angel (photo by Alexander Semenov)

Adult sea angels lack any sort of shell—which they discard when they metamorphose into adulthood.  Their feeding apparatuses can be strangely complicated—pseudoarms and tentacles which recall their cousins the cephalopods. Sea angels are numerous in the oceans but some scientists are concerned that the acidification of the world’s oceans will cause substantial problems for the tiny translucent gastropods.

Sea Angel (Platybrachium antarcticum)

Ye Olde Ferrebeekeeper Archives

October 2021